The present invention relates to hydraulic drive systems for gear-less inter-conversion of rotational energy and gear-less conversion of rotational energy to linear kinetic energy.
Henricson (U.S. Pat. No. 5,657,681) discloses a hydraulic drive system comprising a plurality of hydraulically driven piston units with cam rollers, which are disposed to act against a wave-shaped cam profile of a cam curve element, so that linear movement of the cam rollers against the cam profile produces a relative driving movement between the cam element and the piston units. The characterizing feature of the invention is that the drive system is composed of separate, assembled cam curve element modules and separate assembled piston units.
Reboredo (U.S. Pat. No. 5,689,956) discloses a hydraulic variable speed drive assembly including a hydraulic pump having a cylinder with an associated end cover, a hydraulic motor having a cylinder with an associated end cover, and an intermediate plate with ports or passages for enabling a flow of fluid from the hydraulic pump to the hydraulic motor at a high pressure and from the hydraulic motor to the hydraulic pump at a low pressure, in order to close the circuit. The shafts of the rotors of the hydraulic pump and the hydraulic motor have a common geometric axis, static with respect to the outside, about which they can rotate independently, this rotation being their only possible movement. The variable drive assembly has as its only possible movement, the rotation about a geometric axis fixed with respect to the outside and is different from the geometric axis of the hydraulic pump cylinder, from the geometric axis of the hydraulic motor cylinder, and from the common geometric axis of the rotors. The rotation of the variable drive assembly is effected from the outside and results in that the hydraulic pump cylinder and the hydraulic motor cylinder approach or withdraw their geometric axes with respect to those of their corresponding rotors, thus causing variation of the ratio between the rotation speeds of the hydraulic pump rotor and of the hydraulic motor rotor.
Folsom and Tucker (U.S. Pat. No. 5,956,953) disclose an infinitely variable hydrostatic transmission that includes a radial piston pump having outwardly opening pump cylinders containing radial pump pistons, and a radial piston motor, arranged concentrically around the pump, having inwardly opening motor cylinders containing radial motor pistons. Fluid passages in the transmission intermittently connect the pump cylinders and the motor cylinders in a closed fluid flow circuit. A flexible cam ring is radially interposed between the pump and the motor in load bearing relation to the pump pistons on an inside surface of the cam ring, and in load bearing relation to the motor pistons on an outside surface of the cam ring. An input shaft is coupled in torque driving relation to the pump, and an output shaft is coupled in torque driven relation through a commutator plate to the cam ring. An adjustment mechanism is provided for adjusting the cam ring to a desired radial profile to set the transmission to a desired transmission ratio. A fluid distribution system has passages, including kidney shaped slots through the commutator plate, for fluid flow of fluid pressurized in the pump cylinders to the motor cylinders during a power stroke of the pump and motor pistons, and for fluid flow of spent fluid from the motor cylinders to the pump cylinders during a suction phase of the stroke of the pump and motor pistons. A control system adjusts the profile of the cam ring to control the transmission ratio, and a pressure compensator automatically reduces the transmission ratio when the resistance torque on the output shaft exceeds a predetermined value, as when the vehicle is ascending a steep hill.
These systems use a hydraulic pump and a system of valves to apply hydraulic power to the cam ring. Such valve systems add extra complexity to the design of these systems, and they require associated controlling mechanisms. In addition valve systems introduce some inefficiency into the device, and require maintenance.